Esprit 120 fine focus knob slipping (and Sesto Senso autofocuser as well)

[rofus]

Hi all

I just received my Esprit120 and I'm having a problem I don't know how to solve (and if it's normal).

My imaging train is ASI1600+ZWO wheel 7 positions + PegasusAstro Falcon Rotator + SW field flattener. 

Now problem is that with the scope parked, if I unlock the focus lever at the bottom, the focuser can slide down on its own under gravity if I start focusing outward (and that is something I expect). And if I try to then focus back inward, it works perfectly with coarse knobs, but the fine knob can slip (that is it can turn without actually moving the focuser).

Would not be a problem if it wasn't that as autofocuser for this Esprit120 I bought a Sesto Senso V2. The Sesto Senso works connecting with a coupler on the fine knob bar (once removed both coarse and fine knobs). And it has the same problem of the fine knob...focusing back inward (against force of gravity) sometimes it slips and looses grip.

This is because, once I dismounted, the fine knob is fixed in a round thing bar only by one small grub screw, unlike the coarse knob that has a grub screw actually locking into a flat spot on the bigger coarse focus bar. Sesto Senso adapter as well fixes on the small, round, fine focus bar with two grub screws, and as much as I can tight them (to the point of breaking one but I had replacements), if I turn with my hand the Sesto Senso adaptor, it slips like the fine knob if turning inward agains force of gravity.

Is this a known limitation of fine focus knob and so it means I cannot use Sesto Senso autofocuser? Is weird because my imaging train is not light but definitely is not heavy, and I use the same on a small William Optics 61 with ZWO EAF autofocuser without problems!

Do I need to do something on the focuser itself of the Esprit120? I tried closing a bit, half way, the locking lever of the focuser, but then once it's tight enough to block the focuser from going outward with force of gravity, it means also it's opposing resistance to the fine focus knob, and once again it slips because there locking lever is too tight.

Any help much appreciated...

[Davey-T]

Don't have this scope but if you read the first review of it on the FLO site someone had a problem with the Sesto focuser and adjusted it.

Dave

[Sunshine]

 I have had the same issue with my 115 Orion eon when using heavy eyepieces pointing near zenith, i have discovered a small screw under the focuser which adjusts  tension/friction. By turning this screw inward slightly I was able to stiffen the focuser, it is a fine line between stiffening the focuser and, snagging the fine focus where it slips. Maybe the Esprit may have such a screw under the focuser? there must be.

Edited November 21, 2020 by Sunshine

[rofus]

30 minutes ago, Sunshine said:

 I have had the same issue with my 115 Orion eon when using heavy eyepieces pointing near zenith, i have discovered a small screw under the focuser which adjusts  tension/friction. By turning this screw inward slightly I was able to stiffen the focuser, it is a fine line between stiffening the focuser and, snagging the fine focus where it slips. Maybe the Esprit may have such a screw under the focuser? there must be.

Yeah I read about that screw, if you see attached picture is the first grub screw (the last one before the knob, it's the one slightly out). I tried adjusting it, indeed it makes 'sort of' difference, tight too much and it does worse, if I loose it seems to work, I leave it but then it happens again.

In the attached picture, when the fine knob seems to not move the focus, the ball bearings actually seem to move, even if just a bit. I don't know how that thing works. As I said tightening that small grub scs ew (the first one that is slightly out) changes things a bit, but doesn't solve. If too tight is worst, if I loose it at some point turning the fine knob makes the ball bearings move BUT the outer silver ring/shaft moves and rotates the other way.

I'm shocked that this is not properly setup, I just got it from FLO and checked by Es Reid. I even tried the other grub screw, the second one, but I don't know what it does so I don't want to vary it too much.

[rofus]

49 minutes ago, Davey-T said:

Don't have this scope but if you read the first review of it on the FLO site someone had a problem with the Sesto focuser and adjusted it.

Dave

Read the review, same problem (slipping between fine and coarse knob), but he didn't solve. Tried to connect Sesto Senso to main shaft but that cannot work because sesto senso is made for the fine knob, so less torch and faster steps (the reduction in theory happens on the fine knob).

The real problem is: why an expensive telescope like this has this problem with the fine knob slipping?

[rofus]

Actually I found a video showing exactly the problem:

 

[Sunshine]

As mentioned in this CN post regarding the same issue, the screw i would suspect adjusts the friction should be near the middle of the focuser bottom, i have never encountered a friction adjustment screw off center (at least that I have seen before). Below is a link to the post, have a look at it.

Sky-Watcher Esprit 80 focuser is kinda loose - Refractors - Cloudy Nights

[AKB]

8 hours ago, rofus said:

ASI1600+ZWO wheel 7 positions + PegasusAstro Falcon Rotator + SW field flattener.

This is “light”  ...?

I have a 120, and a Sesto Senso, although an earlier model with a different focuser (serial number 13!). I had the same issue, but adjusted the friction on the focuser.  Whilst looking around at the time for a solution, I found some useful posts here on the forum... including a suggestion to use knicker elastic to counteract the load.

Ill try and find the post...

Tony

Edit: curiously, a search on “knicker elastic” shows 19 posts... it seems to find fairly widespread use amongst the community (‘nuff said!). I didn’t find exactly what I was looking for, but will keep trying.

Edited November 21, 2020 by AKB

[rofus]

17 minutes ago, AKB said:

This is “light”  ...?

I have a 120, and a Sesto Senso, although an earlier model with a different focuser (serial number 13!). I had the same issue, but adjusted the friction on the focuser.  Whilst looking around at the time for a solution, I found some useful posts here on the forum... including a suggestion to use knicker elastic to counteract the load.

Ill try and find the post...

Tony

Edit: curiously, a search on “knicker elastic” shows 19 posts... it seems to find fairly widespread use amongst the community (‘nuff said!). I didn’t find exactly what I was looking for, but will keep trying.

Well light in terms of what it should hold...even if each element was 1kg, and is not being some less than half and some just over half kilo, it would be 1kg less than the max load for focusing. Is probably around 3/3.5kg, and it was behaving better on a cheap William Optics Zenithstar 61...

I tried looking for knickers around :-) I find often used for flats, as I do, but not for counteracting focuser force of gravity. If you could find the post would be useful.

In the meantime will try finding this friction screw...

[rofus]

6 hours ago, Sunshine said:

As mentioned in this CN post regarding the same issue, the screw i would suspect adjusts the friction should be near the middle of the focuser bottom, i have never encountered a friction adjustment screw off center (at least that I have seen before). Below is a link to the post, have a look at it.

Sky-Watcher Esprit 80 focuser is kinda loose - Refractors - Cloudy Nights

On that link in the end they say that they adjust the tension screws..that is all fine in theory, but those adjust the whole focuser tension, and I would not want to touch it as it works perfectly fine in reality with the coarse knobs? 

[wornish]

Had the same issue on my Esprit 100 a few years ago now. As already posted its just a simple adjustment of the tension screw. Worked fine since.   The tension screw only adjusts the friction drive of the fine focuser as far as I remember.

I have the Sesto senso V1 and it is more than capable of holding the weight of my camera and filter holder even when pointing vertically.

[rofus]

2 minutes ago, wornish said:

Had the same issue on my Esprit 100 a few years ago now. As already posted its just a simple adjustment of the tension screw. Worked fine since.   The tension screw only adjusts the friction drive of the fine focuser as far as I remember.

I have the Sesto senso V1 and it is more than capable of holding the weight of my camera and filter holder even when pointing vertically.

Hi Dave,

 

what tension screw do you mean? On other posts mentioned, they talk about the four small tension screws on the top, someone else says say the tension screw visible in my photo (the one protruding out). Which one(s) you adjusted?

I already tried the one visible in my picture, but with no luck...it keeps slipping, and if I tight it even a bit then it doesn’t move anymore...if I losen it a bit and retight a bit, it works for a few rounds then it slips again.

But maybe is not the one you mean?

[AKB]

 

 

[Ken82]

I had a problem with my sesto senso v2 loosing its position night after night on my fsq 106 making auto focusing impossible. 
 

It appears to be working well now with my 85mm scope but I don’t think using the fine focusing knob is ideal for auto focusing. 
 

ken 

 

[rofus]

2 minutes ago, Ken82 said:

I had a problem with my sesto senso v2 loosing its position night after night on my fsq 106 making auto focusing impossible. 
 

It appears to be working well now with my 85mm scope but I don’t think using the fine focusing knob is ideal for auto focusing. 
 

ken 

 

Interesting...I was thinking the same, seems more ideal for light loads, but indeed working on fine knob seems a way to not have to work on a higher torch/higher precision motor but just using the fine knob...that indeed is less robust than the coarse (I might think about mounting the EAF on this and having Sesto Senso on the smaller scope).

 

This morning without changing anything, it doesn't slip.

 

That means one thing: temperature. But from an expensive scope like this and an expensive autofocuser like Sesto Senso I expect something better than that.

 

Scope arrived yesterday very cold, so cold that in the house when I opened the lens cap it was all misty for 1h or so.

 

The question remain: do I have to adjust some tension? And with whicj screws?

 

I applied the elastic band now to help it a bit as well..still, it cannot be the solution for a loadweight that at 3.5kg is far from 'heavy' for such big/expensive system.

[Davey-T]

3 hours ago, rofus said:

it was behaving better on a cheap William Optics Zenithstar 61...

WO Zenithstar  probably had a rack and pinion focuser.

Dave

[wornish]

4 hours ago, rofus said:

Hi Dave,

 

what tension screw do you mean? On other posts mentioned, they talk about the four small tension screws on the top, someone else says say the tension screw visible in my photo (the one protruding out). Which one(s) you adjusted?

I already tried the one visible in my picture, but with no luck...it keeps slipping, and if I tight it even a bit then it doesn’t move anymore...if I losen it a bit and retight a bit, it works for a few rounds then it slips again.

But maybe is not the one you mean?

 

The very small socket headed bolt(screw) shown with red arrow on the photo was very loose.  I just tightened it a little with an allen key and everything now works great.

The bolt I think sets the friction pressure for the fine focusser.

This is for my Esprit 100 so not sure if its the same for the 120.

 

Hope this helps

 

 

Edited November 21, 2020 by wornish

[rofus]

8 minutes ago, wornish said:

 

The very small socket headed bolt(screw) shown with red arrow on the photo was very loose.  I just tightened it a little with an allen key and everything now works great.

The bolt I think sets the friction pressure for the fine focusser.

This is for my Esprit 100 so not sure if its the same for the 120.

 

Hope this helps

 

 

Yes that helps, is the one I tried. It wasn't loose, but I tried tighten it and it was still slipping, till it was too tight and was locked.

 

Then I tried loosening it a bit, and surely then it was too much. I've put it back in a middle way, as it was I think. So yes that is for the fine focus, but wasn't solving the problem in my case.

 

As said this morning without changing anyyhing it was actually all working, that means somehow there's some component that is temperature sensible and was not working properly.

 

So I also added an elastic to make it easier if vertical, now it works but obviously I need to check at different temperatures...

[johnturley]

27 minutes ago, wornish said:

 

The very small socket headed bolt(screw) shown with red arrow on the photo was very loose.  I just tightened it a little with an allen key and everything now works great.

The bolt I think sets the friction pressure for the fine focusser.

This is for my Esprit 100 so not sure if its the same for the 120.

 

Hope this helps

 

 

Dave

Do you know what size Allen key fits this bolt, I have similar problems with the fine focuser on my Esprit 150

I've tightened very slightly the 2 bolts either side of the focuser as shown in the in the photograph below with a 2mm Allen key, to prevent the focuser from slipping, however if you tighten them too much then the fine focuser won't work. You also have to be careful not to slacken them off too much, otherwise I understand that there is a risk that the pressure pads can fall out, which are very difficult to replace.

John 

[rofus]

7 minutes ago, johnturley said:

Dave

Do you know what size Allen key fits this bolt, I have similar problems with the fine focuser on my Esprit 150

I've tightened very slightly the 2 bolts either side of the focuser as shown in the in the photograph below with a 2mm Allen key, to prevent the focuser from slipping, however if you tighten them too much then the fine focuser won't work. You also have to be careful not to slacken them off too much, otherwise I understand that there is a risk that the pressure pads can fall out, which are very difficult to replace.

John 

Hi John

 

do you know if the locking lever at the bottom does basically the same thing?

[johnturley]

6 minutes ago, rofus said:

Hi John

 

do you know if the locking lever at the bottom does basically the same thing?

Partially engaging the locking lever will prevent the focuser from slipping, but if engaged too much then the fine focuser won't work, also was worried that trying to turn the focusing knobs while the locking lever is partially engaged could damage the mechanism.

John 

[wornish]

On 21/11/2020 at 15:29, johnturley said:

Dave

Do you know what size Allen key fits this bolt, I have similar problems with the fine focuser on my Esprit 150

I've tightened very slightly the 2 bolts either side of the focuser as shown in the in the photograph below with a 2mm Allen key, to prevent the focuser from slipping, however if you tighten them too much then the fine focuser won't work. You also have to be careful not to slacken them off too much, otherwise I understand that there is a risk that the pressure pads can fall out, which are very difficult to replace.

John 

Sorry I have no idea,  I have a tin full of assorted Allen keys gained over many years:) It is very small.

The little screw only adjusts the friction of the fine focuser drive on to the coarse shaft.

 

The locking lever simply locks the coarse shaft that's it.  It's not really designed for fine adjustments IMHO.

[SimM]

On 21/11/2020 at 02:40, Sunshine said:

As mentioned in this CN post regarding the same issue, the screw i would suspect adjusts the friction should be near the middle of the focuser bottom, i have never encountered a friction adjustment screw off center (at least that I have seen before). Below is a link to the post, have a look at it.

Sky-Watcher Esprit 80 focuser is kinda loose - Refractors - Cloudy Nights

My micro focuser cover (black) was not attached to the aluminium block inside so it pulled off. An easy check for it slipping is to look through the grub screw hole. If it’s not aligned with the one in the block or it moves then it is loose.

[rofus]

15 minutes ago, SimM said:

My micro focuser cover (black) was not attached to the aluminium block inside so it pulled off. An easy check for it slipping is to look through the grub screw hole. If it’s not aligned with the one in the block or it moves then it is loose.

Thanks, yes actually that is ok in my case.

 

Sorry I forgot to update situation. I spoke with Skywatcher, and also to Primaluce about using my Sesto Senso.

From Skywatcher they say I can correct the focus slip (falling under gravity) tightening the four side screws (as already reported here) or the ones at the bottom, but that would not fix microfocuser.

They say there's indeed a screw for that, as already suggested here, but the basic message was that with a load of 3/3.5kg the microfocuser is NOT ideal.

To confirm that, Primaluce as well said that actually their other focuser Esatto (obviously much more expensive) is the one to use with standard focuser.

Basically the message was that the standard focuser is only good up to a point.

FLO as well said that solution might be to use the coarse knob, so using a different autofocuser.

 

That said, I installed the sesto senso and is working, although if I do a full run inward and outward of the focuser, it doesn't return precisely to 0, so along the line the position shifts a very little bit, but in normal use (movements are much smaller) it works.

 

But is a warning..

[inFINNity Deck]

I had exactly the same issue with my Esprit 150ED and solved it in two ways: first I replaced the 1:10 friction type planetary drive for a home-made 1:16 geared one. Once that was done I created a special tool to open the friction version, cleaned and re-greased it and tightened it until it had enough friction to work again. I now use the friction planetary drive for the rare times that I am visual observing with the scope and the geared one for imaging. The friction one now easily holds my 2" diagonal with the heaviest eyepieces I have, which are around 1.2kg.

More info and pictures on my website.

Nicolàs